High frequency probe

ABSTRACT

A high frequency probe has contact tips located within the periphery of a terminal section of a coaxial cable and shielded by a ground conductor of the coaxial cable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/410,783, filed Apr. 24, 2006, which application claims the benefit ofU.S. Provisional App. No. 60/688,821, filed Jun. 8, 2005.

BACKGROUND OF THE INVENTION

The present invention relates to probe measurement systems for measuringthe electrical characteristics of integrated circuits and otherelectronic devices operated at high frequencies.

There are many types of probing assemblies that have been developed forthe measuring the characteristics of integrated circuits and other formsof microelectronic devices. One representative type of assembly uses acircuit card on the upper side of which are formed elongate conductivetraces that serve as signal and ground lines. A central opening isformed in the card, and a needle-like probe tip is attached to the endof each signal trace adjacent the opening so that a radially extendingarray of downwardly converging needle-like tips is presented by theassembly for selective connection with the closely spaced pads of themicroelectronic device being tested. A probe assembly of this type isshown, for example, in Harmon, U.S. Pat. No. 3,445,770. This type ofprobe does not exhibit resistive characteristics over a broad frequencyrange. At higher frequencies, including microwave frequencies in thegigahertz range, the needle-like tips act as inductive elements and theinductance is not counteracted by a capacitive effect from adjoiningelements. Accordingly, a probing assembly of this type is unsuitable foruse at microwave frequencies due to the high levels of signal reflectionand substantial inductive losses that occur at the needle-like probetips.

In order to obtain device measurements at somewhat higher frequenciesthan are possible with the basic probe card system described above,various related probing systems have been developed. Such systems areshown, for example, in Evans, U.S. Pat. No. 3,849,728; Kikuchi, JapanesePublication No. 1-209,380; Sang et al., U.S. Pat. No. 4,749,942; Lao etal., U.S. Pat. No. 4,593,243; and Shahriary, U.S. Pat. No. 4,727,319.Yet another related system is shown in Kawanabe, Japanese PublicationNo. 60-223,138 which describes a probe assembly having needle-like tipswhere the tips extend from a coaxial cable-like structure instead of aprobe card. A common feature of each of these systems is that the lengthof the isolated portion of each needle-like probe tip is limited to theregion immediately surrounding the device-under-test in order tominimize the region of discontinuity and the amount of inductive loss.However, this approach has resulted in only limited improvement inhigher frequency performance due to various practical limitations in theconstruction of these types of probes. In Lao et al., for example, thelength of each needle-like tip is minimized by using a wide conductiveblade to span the distance between each tip and the supporting probecard, and these blades, in turn, are designed to be arranged relative toeach other so as to form stripline type, transmission line structures.As a practical matter, however, it is difficult to join the thinvertical edge of each blade to the corresponding trace on the card whilemaintaining the precise face-to-face spacing between the blades and thecorrect pitch between the ends of the needle-like probe tips.

One type of probing assembly that is capable of providing acontrolled-impedance low-loss path between its input terminal and theprobe tips is shown in Lockwood et al., U.S. Pat. No. 4,697,143. InLockwood et al., a ground-signal-ground arrangement of strip-likeconductive traces is formed on the underside of an alumina substrate soas to form a coplanar transmission line on the substrate. At one end,each associated pair of ground traces and the corresponding interposedsignal trace are connected to the outer conductor and the centerconductor, respectively, of a coaxial cable connector. At the other endof these traces, areas of wear-resistant conductive material areprovided in order to reliably establish electrical connection with therespective pads of the device to be tested. Layers of microwaveabsorbing material, typically containing ferrite, are mounted about thesubstrate to absorb spurious microwave energy over a major portion ofthe length of each ground-signal-ground trace pattern. In accordancewith this type of construction, a controlled high-frequency impedance(e.g., 50 ohms) can be presented at the probe tips to the device undertest. Broadband signals that are within the range, for example, of DC to18 gigahertz (GHz) can travel with little loss from one end of the probeassembly to another along the coplanar transmission line formed by eachground-signal-ground trace pattern. The probing assembly shown inLockwood et al. fails to provide satisfactory electrical performance athigher microwave frequencies and there is a need in microwave probingtechnology for compliance to adjust for uneven probing pads.

Several high-frequency probing assemblies have been developed forimproved spatial conformance between the tip conductors of the probe andan array of non-planar probe pads or surfaces. Such assemblies aredescribed, for example, in Drake et al., U.S. Pat. No. 4,894,612;Coberly et al., U.S. Pat. No. 4,116,523; and Boll et al., U.S. Pat. No.4,871,964. The Drake et al. probing assembly includes a substrate on theunderside of which are formed a plurality of conductive traces whichcollectively form a coplanar transmission line. However, in oneembodiment shown in Drake et al., the tip end of the substrate isnotched so that each trace extends to the end of a separate tooth andthe substrate is made of moderately flexible non-ceramic material. Themoderately flexible substrate permits limited independent flexure ofeach tooth relative to the other teeth so as to enable spatialconformance of the trace ends to slightly non-planar contact surfaces ona device-under-test. However, the Drake et al. probing assembly hasinsufficient performance at high frequencies.

With respect to the probing assembly shown in Boll et al., as citedabove, the ground conductors comprise a pair of leaf-spring members therear portions of which are received into diametrically opposite slotsformed on the end of a miniature coaxial cable and which areelectrically connected with the cylindrical outer conductor of thatcable. The center conductor of the cable is extended beyond the end ofthe cable (i.e., as defined by the ends of the outer conductor and theinner dielectric) and is gradually tapered to form a pin-like memberhaving a rounded point. In accordance with this construction, thepin-like extension of the center conductor is disposed in a spacedapart, generally centered position between the respective forwardportions of the leaf-spring members and thereby forms, in combinationwith these leaf-spring members, a rough approximation to aground-signal-ground coplanar transmission line structure. The advantageof this particular construction is that the pin-like extension of thecable's center conductor and the respective forward portions of theleaf-spring members are each movable independently of each other so thatthe ends of these respective members are able to establish spatiallyconforming contact with any non-planar contact areas on a device beingtested. On the other hand, the transverse-spacing between the pin-likemember and the respective leaf-spring members will vary depending on howforcefully the ends of these members are urged against the contact padsof the device-under-test. In other words, the transmissioncharacteristic of this probing structure, which is dependent on thespacing between the respective tip members, will vary in an ill-definedmanner during each probing cycle, especially at high microwavefrequencies.

Burr et al., U.S. Pat. No. 5,565,788, disclose a microwave probe thatincludes a supporting section of a coaxial cable including an innerconductor coaxially surrounded by an outer conductor. A tip section ofthe microwave probe includes a central signal conductor and one or moreground conductors, generally arranged in parallel relationship to eachother along a common plane with the central signal conductor, to form acontrolled impedance structure. The signal conductor is electricallyconnected to the inner conductor and the ground conductors areelectrically connected to the outer conductor of the coaxial cable. Ashield member is interconnected to the ground conductors and covers atleast a portion of the signal conductor on the bottom side of the tipsection. The shield member is tapered toward the tips with an openingfor the tips of the conductive fingers. The signal conductor and theground conductors each have an end portion extending beyond the shieldmember and, despite the presence of the shielding member, the endportions are able to resiliently flex relative to each other and awayfrom their common plane so as to permit probing of devices havingnon-planar surfaces.

In another embodiment, Burr et al. disclose a microwave probe thatincludes a supporting section of a coaxial cable including an innerconductor coaxially surrounded by an outer conductor. A tip section ofthe microwave probe includes a signal line extending along the top sideof a dielectric substrate connecting a probe finger with the innerconductor. A metallic shield may be affixed to the underside of thedielectric substrate and is electrically coupled to the outer metallicconductor. Ground-connected fingers are placed adjacent the signal lineconductors and are connected to the metallic shield by way of viasthrough the dielectric substrate. The signal conductor is electricallyconnected to the inner conductor and the ground plane is electricallyconnected to the outer conductor. The signal conductor and the groundconductor fingers (connected to the shield by vias) each have an endportion extending beyond the shield member and, despite the presence ofthe shielding member, the end portions are able to resiliently flexrelative to each other and away from their common plane so as to permitdevices having non-planar surfaces to be probed. While the structuresdisclosed by Burr et al. are intended to provide uniform results over awide frequency range, they unfortunately tend to have non-uniformresponse characteristics at high microwave frequencies.

Gleason et al., U.S. Pat. No. 6,815,963 B2, disclose a probe comprisinga dielectric substrate that is attached to a shelf cut in the undersideof a coaxial cable. The substrate projects beyond the end of the cablein the direction of the longitudinal axis of the cable. A signal tracefor conducting a test signal between the center conductor of the coaxialcable and a probing or contact pad on the device under test (DUT) isformed on the upper side of the substrate. At the distal end of thesignal trace, near the distal edge of the substrate, a via, passingthrough the substrate, conductively connects the signal trace to acontact bump or tip that will be brought into contact with the contactpad of the DUT during probing. A conductive shield which is preferablyplanar in nature is fixed to the bottom surface of the substrate andelectrically connected to the outer conductor of the coaxial cable. Theconductive shield is typically coextensive with the lower surface of thesubstrate with the exception of an aperture encircling the contact tipfor the signal trace. Contact tips may also be provided for contactingground contact pads spaced to either side of the signal probe pad on theDUT. Compared to coplanar type probes, this probe tip provides superiorelectromagnetic field confinement and reduces unwanted coupling or crosstalk between the probe's tips and with adjacent devices. However, athigh frequencies, approximately 220 GHz and greater, the length of theconductive interconnection between the probe tip and the coaxial cableconnection becomes a significant fraction of the wavelength of thesignal and the interconnection acts increasingly as an antenna, emittingincreasingly stronger electromagnetic fields that produce undesirablecoupling paths to adjacent devices. In addition, the conductiveinterconnection comprises a single metal layer deposited on thedielectric substrate and the relatively small section of the conductiveinterconnection limits the current carrying capacity of the probe.

What is desired, therefore, is a probe tip for an on-wafer probeenabling probing at higher frequencies, reducing stray electromagneticfields in the vicinity of the probe tip to reduce cross talk withadjacent devices and capable of conducting a substantial current.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial perspective view of a probe station including a highfrequency probe and a wafer to be tested.

FIG. 2 is an elevation view of an exemplary probe tip portion of a highfrequency probe.

FIG. 3 is a bottom view of the probe tip of FIG. 2.

FIG. 4 is a section view of the probe tip of FIG. 3 along A-A.

FIG. 5 is a section view of the probe tip of FIG. 3 along B-B.

FIG. 6 is a section view of the probe tip of FIG. 3 along C-C.

FIG. 7 is a section view of the probe tip of FIG. 2 along D-D.

FIG. 8 is a section view of the probe tip of FIG. 2 along E-E.

FIG. 9 is a section view of the probe tip of FIG. 2 along F-F.

FIG. 10 is a graphical illustration of crosstalk between a pair of highfrequency probes having tips shorted on a test structure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present inventors considered the probe disclosed by Gleason et al.;U.S. Pat. No. 6,815,963 B2; incorporated herein by reference, andconcluded that while the probe provides superior performance, the highfrequency performance of the probes are constrained by the length of theconductors that interconnect the probe tips and the coaxial cable of theprobe. In a time-varying electromagnetic field, a conductor acts as anantenna radiating electromagnetic energy. For an antenna shorter thanone wavelength of a signal, the radiated power is roughly proportionalto the length of the antenna. The energy radiated by the conductiveinterconnection increases as the frequency of the signal increases andas the fixed length of the interconnecting conductor represents anincreasingly larger fraction of the decreasing wavelength of thesignals. The in-air wavelength of a 220 gigahertz (GHz) signal is 1.3millimeters (mm). The length of the conductive interconnection of theprobe disclosed by Gleason et al. is a significant fraction of thisdistance and substantial electromagnetic fields have been confirmedalong the edges of the dielectric membrane in the vicinity of thecontact tips.

When multiple probes are used for probing in a confined area, such asthe contact pads of an individual device on a wafer, the probe tips comeinto close proximity with one another and energy radiated by the probesproduces capacitive coupling of the probes, normally referred to ascross-talk. Crosstalk increases as the frequency of the signal increasesbecause the energy radiated by the probe increases. The inventorsconcluded that reducing the length of the conductive elements in theprobe tip would reduce the electromagnetic fields emanating from thecontact tip area of the probe, reducing cross-talk with adjacentdevices, and increasing the frequency at which the probe would beuseful.

Referring in detail to the drawings where similar parts of the probe areidentified by like reference numerals and, more particularly to FIGS. 1,2 and 3, a high frequency probe 20 is designed to be mounted on aprobe-supporting member 22 of a probe station so as to be movable to asuitable position for probing a device-under-test (DUT), such as anindividual component on a wafer 24. In this type of application, thewafer is typically restrained on the upper surface of a chuck 26 whichis part of the same probe station. The upper surface of the chuckcommonly includes a plurality of apertures that are selectivelyconnectible to a source of vacuum. When vacuum is connected to theapertures, air pressure on a wafer, resting on the upper surface of thechuck, secures the wafer to the chuck's surface. Ordinarily an X-Y-Zpositioning mechanism, such as a micrometer knob assembly, is providedto effect movement between the supporting member 22 and the chuck 26 sothat the contact tips 28 of the probe can be brought into pressingengagement with contact or probing pads 30 on the wafer. The contactpads typically comprise a signal contact pad and at least one groundcontact pad for a particular component 32 requiring measurement. Acommon contact pad arrangement comprises a centrally located signalcontact pad flanked by a pair of ground contact pads, also referred as aGSG (ground-signal-ground) probing configuration.

The exemplary high frequency probe 20 has a port which, in the preferredembodiment depicted, comprises a waveguide 34 having a flanged connector36. The flanged connector enables selective connection, through a matingflanged connector 38, to an external waveguide 40 connecting the probeto the measuring instrumentation. The waveguide is connected to aprimary support block 42 of the probe which, in the preferred embodimentshown, is made of brass and is suitably constructed for connection tothe probe-supporting member 22. To effect connection to theprobe-supporting member, a round opening 44 that is formed on the blockis snugly and slidably fitted onto an alignment pin (not shown) thatprojects upward from the probe-supporting member. A screw 46 is insertedinto each of a pair of countersunk openings 48 provided in the block.The screws engage corresponding threaded apertures in theprobe-supporting member to secure the probe to the supporting member.

A semi-rigid coaxial cable 50 is retained in the primary support block42 and is connected, within the block, to the waveguide 34 by a coaxialcable-to-waveguide transition; such the adjustable backshort disclosedby Martin, U.S. Pat. No. 6,549,106 B2, incorporated herein by reference.In the preferred embodiment, the semi-rigid coaxial cable 50 has anominal outer diameter of 0.584 mm (0.023 inches) and comprises anaxially extending silver plated copper center conductor 70 and a coaxialcopper outer conductor 72 separated from the center conductor by anair-expanded Teflon™ dielectric 74. One suitable type of cable, forexample, is available from Micro-coax Components Inc. of Pottstown, Pa.under model number UT-020.

The end portion of the cable 50 projecting from the support blockremains freely suspended and, in this condition, serves as a movablesupport for the contact tips 28 of the probe. A portion of the cableprotruding from the primary support block is bent downwardly and isterminated in an oblique terminal section 74 formed by cutting thecoaxial cable at an oblique angle. While the oblique angle could be anyconvenient angle, the angle is typically the complement of angle of thedownward sloping portion of the coaxial cable so that when the probe isinstalled in a probe station the substantially planar oblique terminalsection 74 will be aligned substantially parallel to the top surface ofthe chuck 26.

The inventors concluded that to reduce the stray electric fields(“E-fields”) and magnetic fields (“H-fields”) in the vicinity of theprobe tip the distance between the ends of the contact tips and theconductors of the coaxial cable should be minimized and the contact tipsshould be located in an area shielded by the outer conductor of thecoaxial cable. The contact pads of devices commonly tested in probestations are commonly arranged in rows with a centrally located signalcontact pad flanked by a pair of ground contact pads, a GSG(ground-signal-ground) arrangement. The three contact tips 76, 78, 80 ofthe exemplary probe 20 correspond to a GSG arrangement for contacts padswith the central contact tip 80 of the exemplary probe, the signal tipof the GSG arrangement, conductively connected to the center conductor70 of the coaxial cable 50 and the flanking contact tips 76, 78, oneither side of the central contact tip, conductively connected to theouter conductor 72 of the coaxial cable which is connected to a ground.However, other arrangements of contact tips corresponding to otherarrangements of contact pads, for examples a GSSG(ground-signal-signal-ground) arrangement, an SGS (signal-ground-signal)arrangement or an SGGS (signal-ground-ground-signal) arrangement, may beused. To improve shielding and reduce the lengths of conductiveconnections to the coaxial cable, the contact tips of the high frequencyprobe 20 are located within the periphery of the coaxial cable and, morespecifically, within the periphery of the oblique terminal section 74 ofthe coaxial cable.

When positioning the contact tips of a probe in a probe station, theoperator typically observes the contact tips of the probe and thecontact pads of the DUT through a microscope that is positioned abovethe DUT. To minimize the conductor length while enabling visualobservation of the contact tips, the end portion of the coaxial cablefurther comprises a second oblique section 82 produced by cutting thecoaxial cable at a second oblique angle, typically normal to the obliqueterminal section 74. The second oblique section 82 intersects theoblique terminal section 74 adjacent to the edge of the contact tips 76,78, 80 enabling the operator to view the edges of the contact tips fromabove.

Referring to FIGS. 4, 5, 6, 7, 8 and 9, the tip portion of the probe 20further comprises a planar upper dielectric substrate 84 affixed to thecoaxial cable 50 and having an upper surface abutted to the obliqueterminal section 74 of the cable. The upper dielectric substrate may beaffixed to the coaxial cable by, for example, an epoxy adhesive appliedto the upper surface of the substrate along the periphery of the cableand solder joining metallic vias 102, 104, 106, 108 in the substrate tothe metallic outer conductor 72 of the cable. The upper dielectricsubstrate 84 has a lower surface which is bonded to, by plating orotherwise, an upper surface of an upper conductive layer 86, comprisingthree typically metallic, conductively disconnected regions 130, 132,134. The lower surface of the upper conductive layer 86 is, in turn,bonded to an upper surface of a lower dielectric layer 88 and a lowerconductive layer 90 is bonded to the lower surface of the lowerdielectric layer. The contact tips 76, 78, 80, which may comprisemetallic bumps or buttons, are formed on or conductively affixed to thelower surfaces of respective portions of the lower conductive layer 90.

The lower conductive layer 90 comprises three conductive, typicallymetallic, regions 92, 94, 96 that are not conductively connected to eachother. A first region 92 includes a portion, at least partially,spatially coinciding with and conductively connected to the centralcontact tip 80, the signal contact tip of the GSG probe arrangement. Thesecond 94 and third 96 regions of the lower metallic layer arerespectively conductively connected to a contact tip 76, 78 located oneither side of the central tip. The second 94 and third 96 regions ofthe lower conductive layer 90 are conductively connected to the outerconductor 72 of the coaxial cable 50 which is connected to a ground inthe typical GSG probing arrangement. The second 92 and third 94 regionsof the lower conductive layer effectively extend the outer conductor ofthe coaxial cable to the immediate vicinity of the signal contact tipforming a conductive shield that extends over an area of the cable'sterminal section that is substantially larger than the area of theground contact tips and proximate to the signal contact tip 80. Theconductive shield confines electromagnetic radiation in the immediatearea of the contact tips.

The central contact tip 80 is conductively connected to the centerconductor 70 of the coaxial cable by conductors that are arranged withinthe periphery of the terminal section of the coaxial cable and extendthrough the upper and lower dielectric layers and the upper conductivelayer. A conductive via 120 in the lower dielectric layer 88 that is atleast partially spatially coincident with and conductively connected tothe first region 92 of the lower conductive layer 90 connects the firstregion of the lower conductive layer to a first region 130 of the upperconductive layer 86. A conductive via 110 in the upper dielectricsubstrate 84 that is, at least partially, spatially coincident with andconductively connected to the first region 130 of upper conductive layer86 conductively connects the first region of the upper conductive layerand the central contact tip 80 to the center conductor 70 of the coaxialcable 80. The cross-sections of the conductive interconnection of thecentral contact tip 80 and the coaxial cable are substantially greaterthan that of a conductor comprising a single metal layer deposited on asubstrate permitting higher current to be transmitted by the contacttips.

Similarly, the flanking contact tips 76, 78 are conductively connectedto the outer conductor of the coaxial cable 50 by respective conductivevias 124, 122 in the lower dielectric layer 88 that are, conductivelyconnected to, respective, second 96 and third 94 regions of the lowerconductive layer 90 and with the corresponding second 132 and third 134regions of the upper conductive layer 86. Conductive vias 102, 104 and106, 108 in the upper dielectric layer 84 provide a conductiveconnection between the second 132 and third 134 regions of the upperconductive layer 84 and the outer conductor 72 of the coaxial cable 50.The conductive connections from the flanking contact tips to the outerconductor of the coaxial cable are arranged substantially with theperiphery of the terminal section of the cable enabling pluralities ofprobes to be used to probe of areas.

Stray E-fields in the area of the probe tip produce capacitive couplingto or crosstalk with adjacent devices at frequencies well below theresonant frequency of the probe tip. The crosstalk worsens as thefrequency of the signal increases and the stray fields strengthen. Atany particular frequency, the worst case crosstalk occurs when adjacentprobes are terminated with short circuits on a test substrate. FIG. 10graphically illustrates tip-to-tip crosstalk between a pair highfrequency probes, exemplified by the high frequency probe 20, at signalfrequencies up to 40 GHz. FIG. 10 records tip-to-tip crosstalk for twohigh frequency probes with probe tips separated by 150 micrometers (μm)on a continuous ground structure. Exemplary values of tip-to-tipcrosstalk for the high frequency probes are −58 dB at 15 GHz andapproximately −51 dB at 30 GHz. Over the frequency range of 5 to 40 GHz,the tip-to-tip crosstalk of the high frequency probes is approximately10 dB less than probe tips of the type disclosed by Gleason et al.

The conductive connections between the contact tips and the conductorsof the coaxial cable of the high frequency probe are substantiallyshorter than the conductive interconnections of prior probes reducingthe conductor length-to-wavelength ratio and the power radiated by theprobe's conductors when high frequency signals are applied. In addition,the high frequency probe incorporates shielding for the contact tips toconfine energy radiated from the area of the probe tip. The useablefrequency range of the probe is extended and crosstalk to adjacentprobes is substantially reduced by the reduction in and confinement ofenergy radiated from the vicinity of the probe tip. Moreover, thecross-sections of the conductive interconnections from the contact tipsto the coaxial cable are substantially greater than the cross-sectionsof the single layer conductive interconnections of prior probessubstantially increasing the current carrying capacity of the probe.

The detailed description, above, sets forth numerous specific details toprovide a thorough understanding of the present invention. However,those skilled in the art will appreciate that the present invention maybe practiced without these specific details. In other instances, wellknown methods, procedures, components, and circuitry have not beendescribed in detail to avoid obscuring the present invention.

All the references cited herein are incorporated by reference.

The terms and expressions that have been employed in the foregoingspecification are used as terms of description and not of limitation,and there is no intention, in the use of such terms and expressions, ofexcluding equivalents of the features shown and described or portionsthereof, it being recognized that the scope of the invention is definedand limited only by the claims that follow.

1. A probe comprising: (a) a coaxial cable including an axiallyextending first conductor, a coaxial second conductor and a dielectric,said coaxial cable terminating in an oblique terminal section; (b) adielectric substrate affixed to said coaxial cable with a first sideproximate said terminal section and a second side remote from saidterminal section; (c) a first conductive member conductively connectingsaid first conductor to a first contact located on said second side ofsaid dielectric substrate and substantially within a periphery of saidterminal section, said first contact engageable with a device to betested; and (d) a second conductive member conductively connecting saidsecond conductor to a second contact located on said second side of saiddielectric substrate and substantially within said periphery of saidterminal section.
 2. The probe of claim 1 wherein said first conductivemember is located substantially within said periphery of said terminalsection.
 3. The probe of claim 2 wherein said second conductive memberis located substantially within said periphery of said terminal section.4. The probe of claim 1 further comprising a third contact conductivelyconnected to said second conductor and located substantially within saidperiphery of said terminal section on said second side of saiddielectric substrate.
 5. The probe of claim 4 wherein said conductiveconnection of said third contact to said second conductor is locatedsubstantially within said periphery of said terminal section.
 6. Theprobe of claim 1 wherein said oblique terminal section comprises: (a) afirst oblique substantially planar section of said coaxial cable; and(b) an intersecting second oblique section of said coaxial cable.
 7. Theprobe of claim 6 wherein said second oblique section intersects saidfirst oblique planar section proximate said first contact.
 8. The probeof claim 6 wherein said second oblique section is substantially normalto said first oblique planar section.
 9. The probe of claim 1 whereinsaid second conductive member further comprises a planar portionadjacent to but free of conductive connection with said first contact.10. The probe of claim 9 wherein said second conductive member isconductively connected to a ground.
 11. The probe of claim 1 whereinsaid dielectric substrate comprises: (a) a first dielectric layer havinga first side and a second side; (b) a conductive layer having a firstside in contact with said second side of said first dielectric layer anda second side; and (c) a second dielectric layer having a first side incontact with said second side of conductive layer and a second side. 12.The probe of claim 1 wherein one of said first and said secondconductive members comprises: (a) a contact tip; and (b) a substantiallyplanar conductive shield conductively connected to said contact tip andelectrically isolated from the other of said first and said secondconductive members, said conductive shield coextensive with a greaterarea of said terminal section than an area of said contact tip.
 13. Aprobe comprising: (a) a coaxial cable including an axially extendingfirst conductor and a coaxial second conductor (b) a first contact tipconductively connected to said first conductor; and (c) a second contacttip conductively connected to said second conductor, crosstalk betweensaid second contact tip of said probe and a contact tip of ansubstantially similar probe, spaced 150 micrometers apart on a groundstructure from said second contact, being less than −42 dB for anapplied signal frequency of 30 gigahertz.
 14. The probe of claim 11wherein said crosstalk is less than −47 dB for said applied signalfrequency of 30 gigahertz.
 15. The probe of claim 11 wherein saidcrosstalk is less than −50 dB for said applied signal frequency of 30gigahertz.
 16. A probe comprising: (a) a coaxial cable including anaxially extending first conductor, a coaxial second conductorconductively connected to a ground, and a dielectric, said coaxial cableterminating in an oblique terminal section; (b) a first contact locatedsubstantially within a periphery of said terminal section andconductively connected said first conductor, said first contactengageable with a device to be tested; and (c) a conductive memberconductively connecting said second conductor to a second contactlocated substantially within said periphery of said terminal section,said conductive member including a substantially planar conductorlocated proximate to but conductively disconnected from said firstcontact.
 17. The probe of claim 16 wherein said conductive member islocated substantially within said periphery of said terminal section.18. The probe of claim 16 further comprising a second conductive memberconductively connecting said second conductor to a third contact locatedsubstantially within said periphery of said terminal section, saidsecond conductive member including a substantially planar conductorlocated proximate to but conductively disconnected from said firstcontact.
 19. The probe of claim 16 wherein said oblique terminal sectioncomprises an oblique substantially planar first section of said coaxialcable intersected by a second oblique section of said coaxial cable. 20.The probe of claim 19 wherein said second oblique section intersectssaid first section proximate said first contact.